1. Field of the Invention
The present invention relates to a reclining device of two-point hinged type for use in a vehicle seat, which has a reclining hinge, a center of rotation about which a seat back of the seat is rotatively and adjustably inclined to a desired angle and a folding hinge, a center of rotation about which the seat back is rotatively folded.
2. Description of Prior Art
A two-point hinged structure has been employed in a vehicle seat to provide a lower hinge point about which a seat back is rotatively reclined and an upper hinged point about which the seat back is folded down to or unfolded from a seat cushion. As typically known from the two Japanese Laid-Open Patent Publications Nos. 9-286264 and 11-75980 for instance, this kind of two-point-hinged reclining device is effective in allowing the seat back to be folded down to a substantially horizontal line with respect to the seat cushion, while maintaining its original reclining functions.
Specifically, reference is made to FIG. 8 which shows an elevational side view which roughly shows a structure of the above-stated conventional two-point hinged type of reclining device (110) provided in a vehicle seat. According thereto, a reclining plate element (112) is at the lower end portion thereof pivotally connected via a lower hinge pin (118) with the backward end portion of a base frame member (116) in a seat cushion (114), and is at the upper end portion thereof pivotally connected via an upper hinge pin (122) with the lower end portion of a seat back frame member (121) in a seat back (120). Hence, the seat back (120) may be adjustably inclined about the lower hinged point (at 118) in forward and backward directions, and further be folded about the upper hinged point (at 122) from a substantially vertical use position indicated by one-dot chain line down to a slightly sloped non-use position indicated by the two-dot chain line.
Designation (124) denotes a reclining lock mechanism for locking the seat back (120) to a desired inclined angle and releasing the seat back therefrom. Designation (126) denotes a folding lock mechanism for locking the seat back (120) to the non-use position and releasing the seat back from that non-use position.
In this sort of reclining device, as described in the foregoing Japanese Laid-Open Patent Publication No. 9-286264, there is normally provided a lock mechanism or stopper means for limiting the forward inclination of seat back at a predetermined angle relative to the reclining plate (at 112) in light of safety reasons. That is, referring again to FIG. 8, normally, unless the reclining plate (112) is inclined by a particular angle, a user has to unlock the seat back (120) via the folding lock mechanism (126) and incline it forwardly. But, as indicated by the two-dot chain lines in the FIG. 8, the forward inclination of the seat back (120) relative to the upper hinge point (at 122) is prevented by the foregoing safety lock or stopper means (not shown) so that the seat back (120) is only inclined to the upwardly sloped state as shown, with the result that the seat back (120) can not be folded down onto the seat cushion (114) and therefore the back surface (120a) thereof is not positioned on a substantially horizontal line. In that case, in addition to the afore-said folding lock operation, it is further required for the user to operate the reclining lock mechanism (124) to unlock the seat back (120) from the current reclining locked state and incline it forwardly to a substantially horizontal line. This apparently results in troublesome intricate operations being required on the user's side.
Incidentally, there has been known a dual lock mechanism, (as disclosed by the Japanese Laid-Open Patent Publication No. 2003-319847 for instance), which is normally provided in a pair of ordinary reclining devices (the so-called dual reclining device) of one-point hinged type wherein each of the two reclining device has an arm which is pivotally connected via one hinge pin with the corresponding one of two side frame members of seat cushion frame, the arm having upper end connected with a seat back frame. This dual lock mechanism includes a pair of lock elements which are operatively provided in the respective two ordinary reclining devices so as to be operable in a synchronized manner for locking and unlocking both of the two reclining devices. As suggested in the above-noted Japanese Laid-Open Patent Publication No. 11-75980, it is preferable to provide such dual reclining lock mechanism to the two-hinge point type of reclining device stated above. But, as this sort of reclining device has been with the above-described problems, it is technically difficult to incorporate the dual reclining lock mechanism therein.